The SSH2 protocol includes the ClientAliveInterval and ClientAliveCountMax options. The sshd_config man page describes both:

ClientAliveInterval
Sets a timeout interval in seconds after which if no data has been received from the client, sshd will send a message through the encrypted channel to request a response from the client. The default is 0, indicating that these messages will not be sent to the client. This option applies to protocol version 2 only.

ClientAliveCountMax
Sets the number of client alive messages which may be sent without sshd receiving any messages back from the client. If this threshold is reached while client alive messages are being sent, sshd will disconnect the client, terminating the session. It is important to note that the use of client alive messages is very different from TCPKeepAlive. The client alive messages are sent through the encrypted channel and therefore will not be spoofable. The TCP keepalive option enabled by TCPKeepAlive is spoofable. The client alive mechanism is valuable when the client or server depend on knowing when a connection has become inactive.

TinyTERM Plus responds to the keepalive packets sent when ClientAliveInterval is non-zero. Thus, it does not automatically get disconnected when idle.

CR 653, added in version 4.8.1

This entry was posted on Monday, April 30th, 2007 at 2:01 pm and is filed under SSH. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.